Method of starting once-through type boilers



March 15, ZENSUKE TAMURA METHOD OF STARTING ONCE-THROUGH TYPE BOILERSFiled Dec. 5, 1963 Fig.

VALVE TURBINE DETECTOR 1 m CONDENSER 2 I F H I I 5% 5 L I .J I BOILERDEAERATOR Fig. 2

Flowouf rafe 0f flu/0 Time Fig. 3 F ue/ rafe ATTORNEY United StatesPatent Olhce 3,24%,187 Patented Mar. 15, 1966 METHOD OF STARTHNGflNCE-TERQUGH TYPE BOILERS Zensulre Tamara, Hitachi-sin, Japan, assignorto Hitachi, Ltd Tokyo, Japan, a corporation of Japan Filed Dec. 3, 1963,Ser. No. 327,639

Claims priority, application Japan, Dec. 4, 1962,

$763,658 2 Claims. (Cl. 122-406) This invention relates to once-throughtype boilers, and more particularly to method or process of startingoperation of such type of boiler plants.

As is well-known, in starting operation of boiler plants of once-throughtype, the so-called water swelling phenomena is inevitable, andnecessitates the use of piping of larger capacity than that requiredduring normal operation when such phenomena does not occur at all,resulting in poor economy.

An object of the present invention is to provide method or process ofstarting operation of boiler plants of the kind specified, in which thewater swelling phenomena is substantially prevented from occurring.

Another object of the present invention is to provide method or processof starting operation of boiler plants of the kind specified, whereinpeak values in the rate of water flowing out during the water swellingphenomena are so low that the capacity of the bypass piping can beremarkably smaller than ever.

There are other objects and particularities of the present invention,which will best be understood from the following detailed description ofthe invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a boiler plant of through-flow type, inwhich the present invention is carried out;

FIG. 2 is a curve diagram showing relations between the flowing-out rateof water or working medium and the fuel rate during starting of theboiler plant shown in FIG. 1, as well as the plant modified according tothe present invention; and

FIG. 3 shows characteristic curves of the boiler plants embodying thepresent invention.

A typical boiler plant of once-through type is schematically shown inFIG. 1 of the accompanying drawings, and comprises a feed water pump 1for supplying highpressure water to a boiler 2, a secondary superheater3 for generating high-pressure steam, a turbine 11 actuated thereby, acondenser 12, a condenser pump 13, and a deaerator 14 connected beforethe pump 1. Though not illustrated, there may be provided a feed-waterheater before the pump 1 for preheating feed water by utilization ofexhaust steam.

The boiler plant shown in FIG. 1 is also provided with a superheaterbypass circuit and a turbine bypass circuit connecting the inlet andoutlet or" secondary superheater 3 with the condenser 12, and thesecomprising a superheater bypass valve 5, a turbine bypass valve 7, pipe6', a flash tank 8, a path 18 including a dump valve 9 for passing steamfrom flash tank 8 to the steam chamber of condenser 12, and a path 19including a drain valve for passing saturated water from flash tank 8 tothe hot well of condenser 12.

During the period of starting of the once-through type boiler plant asshown in FIG. 1, when the boiler output is low and steam cannot begenerated in a predetermined state, the turbine, or the superheater andturbine, are usually by-passed by way of the above-referred circuits forcirculating generated steam directly through the condenser 12. In such atype of boiler plants, undesirable water swelling occur during startingoperations.

At the start of such a type of boiler plant, the heat absorption rate isgenerally first maximum in the waterwall portion of the boiler, so thatthe temperature of the water rises very quickly at the outlet of thewater wall, and before the water at the outlet of boiler would havereached saturation temperature, the water in the waterwall portionreaches saturation temperature, resulting in undesirable expansion ofwater therein, which forces a large amount of water at undersaturationtemperature to flow into the bypass circuit through the valve 5.

In avoiding serious problems resulting from this water swellingphenomena a superheater bypass valve 5 and a turbine bypass valve 7 areutilized for maintaining the pressure of circulatory system constant.Thus, when the system pressure rises, the condition is detected bypressure detector 20 and the opening of valves 5 and 7 will be increasedto prevent the pressure rise, so that they serve as safety valves duringnormal operation of the boiler plant. Consequently, when the flow-outrate of water is extraordinarily increased as in the case of the waterswelling phenomena, the valves 5 and 7 are caused to increase theiropening for preventing pressure rise in the system, but in order toenable such a pressure rise to be prevented, the valve opening, as wellas, the piping should be remarkably large, resulting in poor economy.

The present invention proposes to provide means in connection with themethod or process of starting such a type of boiler plant, whereby thepeak value of flow-out rate of water is decreased during the period whenthe water swelling would otherwise occur, so that the bypass piping andthe bypass valves required by virtue of such phenomena may be ofdecreased capacity.

The superheater bypass valve 5 and the tunbine bypass valve '7 increasetheir opening automatically when the system pressure rises in responseto control from pressure detector 2%, such action being of particularlyincreased speed or response and of increased opening when water swellingoccurs. The present invention provides for control between the bypassvalves 5 and '7 and the fuel regulating valve 16, so that the tension ofincreased pressure due to water swelling by valves 5 and 7 results in anautomatic decrease in the rate at which fuel is supplied to the burner15, and when the valve-closing actuation is commenced, the fuel systemis returned to normal automatically.

In FIG. 2, the solid-line curves show the relation between fuel rate andflow-out rate of fluid at the boiler outlet in old boiler plants, whiledotted-line curves show the corresponding relation in a boiler plantembodying the present invention. The relation between fuel rate andsuperheater-bypass-valve opening obtained when the present invention isembodied is shown in FIG. 3. It will eadily be understood from thesecurve diagrams that, when the fuel rate is decreased, upon occurrence ofwater swelling according to the present invention the flow-out rate offluid is remarkably decreased, and the maximum opening of bypass valve 5and piping capacity may be decreased remarkably, resulting in goodeconomy.

-In PEG. 1, a suitable control system for automatic starting operationaccording to the present invention is shown by dotted lines, whereby theopening degrees of bypass valves 5 and 7 are automatically detected byvalve detectors 21 and 22, respectively, and only when their openinghave increased extraordinarily or beyond predetermined degrees, the fuelsupply is automatically decreased. In practice, such a control system asabove outlined may be provided utilizing well-known control elements andcombinations which are illustrated schematically in FIG. 1 as detectors21 and 22. When the fuel system includes a relatively large operationaltime-lag, as when coal is used as the boiler fuel, the temperature ofwater wall or evaporator that would have reached the saturationtemperature might be used as the control for decreasing the rate ofsupply of boiler fuel.

Thus, according to the present invention, the variation of flow-out rateof working medium is reduced, so that the piping capacity may bedecreased remarkably with smallerdiameter pipes and smaller valves,resulting in good economy. In addition water swelling may be suppressedor prevented, so that starting operations can be effected in a stableand smooth manner.

What I claim is:

1. The method of controlling the starting operation to effectivelyreduce water swelling in a once-through type boiler circuit including aboiler having a burner, a turbine, a superheater connected between saidboiler and the input side of said turbine, a condenser connected to theexhaust side of said turbine, and bypass means including a valve forconnecting the output of said boiler directly to said condenser inresponse to detection of increased pressure in said boiler, the methodcomprising during passage of water through said bypass means with saidvalve in the open condition in response to the pressure of said water,

detecting the amount of water flowing through said bypass means by thedegree of opening actuation of said valve,

decreasing the rate of fuel supplied to said burner only in response todetection of the amount of water flowing through said valve above alimit representing an indication of the initial stages of water swellingin said boiler, and

restoring the normal rate of fiow of fuel to said boiler upon reductionof said water flow below said limit as determined by the reduced degreeof opening actuation of said valve.

2. The method of controlling the starting operation to effectivelyreduce water swelling in a once-through type boiler circuit including aboiler having a burner; a turbine, a superheater connected between saidboiler and the input side of said turbine, a condenser connected to theexhaust side of said turbine, and bypass means for connecting the outputof said boiler and said superheater directly to said condenser inresponse to detection of increased pressure in said boiler includingfirst and second pressure responsive valves controlling the flow fromsaid boiler and said superheater into said bypass means, respectively,the method comprising during passage of water through said bypass meanswith both said first and second valves in the open condition in responseto the pressure of said water,

detecting the amount of water flowing through said bypass means by thedegree of opening actuation of both valves, decreasing the rate of fuelsupplied to said burner only in response to detection of the amount ofwater flowing through said valves above a limit representing anindication of the initial stages of water swelling in said boiler, andrestoring the normal rate of flow of fuel to said boiler upon reductionof said water flow below said limit as determined by the reduced degreesof opening actuation of said valves.

References Cited by the Examiner UNITED STATES PATENTS 2,900,792 8/1959Buri 122-406 3,035,557 5/ 1962 Litwinoff 122406 3,055,181 9/1962Argesinger et al. 122406 FOREIGN PATENTS 879,032 10/ 1961 Great Britain.

OTHER REFERENCES German printed application No. 1,103,348, printed Mar.30, 1961.

German printed application No. 1,109,705, printed June 29, 1961.

Publication: Large Sub and Supercritical Steam Generator Startup andControl System Integration with the Turbine Generator, by C.Strohrneyer, Jr. Reprint of paper represented at American PowerConference, Mar. 29, 1962, Chicago, Ill. (Pages 6-10 and Figs. 5-10, 4pp. in particular) FREDERICK L. MATIESON, JR., Primary Examiner.

KENNETH W. SPRAGUE, ROBERT A. OLEARY,

Examiners.

1. THE METHOD OF CONTROLLING THE STARTING OPERATION TO EFFETIVELY REDUCEWATER SWELLING IN A ONCE-THROUGH TYPE BOILER CIRCUIT INCLUDING A BOILERHAVING A BURNER, A TURBINE, A SUPERHEATER CONNECTED BETWEEN SAID BOILERAND THE INPUT SIDE OF SAID TURBINE, A CONDENSER CONNECTED TO THE EXHAUSTSIDE OF SAID TURBINE, AND BYPASS MEANS INCLUDING A VALVE FOR CONNECTINGTHE OUTPUT OF SAID BOILER DIRECTLY TO SAID CONDENSER IN RESPONSE TODETECTION OF INCREASE PRESSURE IN SAID BOILER, THE METHOD COMPRISINGDURING PASSAGE OF WATER THROUGH SAID BYPASS MEANS WITH SAID VALVE IN THEOPEN CONDITION IN RESPONSE TO THE PRESSURE OF SAID WATER, DETECTING THEAMOUNT OF WATER FLOWING THROUGH SAID BYPASS MEANS BY THE DEGREE OFOPENING ACTUATION OF SAID VALVE, DECREASING THE RATE OF FUEL SUPPLIED TOSAID BURNER ONLY IN RESPONSE TO DETECTION OF THE AMOUNT OF WATER FLOWINGTHROUGH SAID VALVE ABOVE A LIMIT REPRESENTING AN INDICATION OF THEINITIAL STAGES OF WATER SWELLING IN SAID BOILER, AND RESTORING THENORMAL RATE OF FLOW OF FUEL TO SAID BOILER UPON REDUCTION OF SAID WATERFLOW BELOW SAID LIMIT AS DETERMINED BY THE REDUCED DEGREE OF OPENINGACTUATION OF SAID VALVE.